Reflex klystrons



pril 16, 1957 P. .lANlsV 2,789,249

REFLEX KLYsTRoNs Filed June 1, 1951 ATTO RN EY United States Patent O REFLEX KLYSTRONS Peter Janis, Bayside, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application June 1, 1951, Serial No. 229,431

7 Claims. (Cl. 315-518) l The present invention relates to a type of electronbeam device commonly termed Ithe klystron and more particularly to that type of klystron in which the electronbeam is passed lthrough the interaction space of a resonator and is then reected so as to 1re-enter the resonator for renewed interaction.

In this type of klystron, an electron-beam is ordinarily formed and accelerated by an electron gun, and this beam is passed through two apertured walls forming part of a space resonator, toward a reector electrode so as to be repelled and reversed in its travel, and to -re-enter the interaction space of the same resonator. The physical proportions of the resonator and the voltage on the reflector largely determine the operating frequency of the reex klystron.

It -is desirable that the operating frequency shall be susceptible to definite control, and that a certain definite frequency will result from adjustments made according to a previous calibration. However, with reflex klystrons of a construction commonly employed heretofore, a ditiiculty has been encountered, termed moding, i. e., variations in frequency to be effected by changing the operating conditions sometimes ydo not result, but instead the klyst-ron commences operation at a very different frequency from that intended, the device then operating in a different mode.

The presen-t invention resides in the discovery of what is believed to be a cause of moding and in the elimination of that diiculty. I have found that if a magnetic field is impressed on the yelectron-beam transverse to its path as it initially passes through the interaction space of the resonator, the moding can largely be eliminated. From this, I am convinced that moding results from a disturbance in the beam-forming region prod-need lby the bunched electron-beam after being returned by the reflector. The electron-beam, when bent by the transverse magnetic field, operates as intended in respect to velocity modulation, bunching, and interaction with the resonator; but because it does not retrace its original course, the returning electron-beam `does not harmfully interact with the newly formed electron-beam in the gun. This effect is further assured by diverting the reflected hunched beam to a region where the returning electrons, after passing through the interaction space, are actually collected Ibefore reaching the beam-producing region.

The nature of the invention and its further features of novelty will be better appreciated from the following detailed disclosure of two illustrative embodiments thereof which are shown in the accompanying drawings. In those drawings:

Figure l is a lateral view, partly in cross-section, of one illustrative embodiment yof the invention and Figure 2 is a similar view of a second embodiment.

Figure 3 is a greatly enlarged view illustrating the theory of operation of the tubes shown in Figures l and 2.

Referring now to Figure 1, a resonator is shown having outer wall and an inner wall 12 Whose effective axial length is adjusted by slida-ble tuner 14. An electron discef as electron permeable portions of the resonator wall, or,. Electrodes.

more generally, as elect-ron permeable walls. 16 and 18 are hermetically sealed so as to extend through the wall of an insulating evacuated envelope 20.

action space a reliector electrode 24 is supported and provided with an external terminal 24a.

resonator.

Gun 22 includes a 34 is connected to the grid 16 and operates at the same D.C. potential. The shield may operate at or near cathode potential, while grids 34, y16 and 18 opera-te at a. high positive voltage and reflector 24 operates at a suit` able negative voltage.

A uniform beam yof electrons is accordingly projected from the gun through the interaction space. Instantaneous differences in high frequency potentials, `existing between portions 16a and 18a, impress velocity modulation on the forward electron-beam. After emerging from portion 18a, this velocity modulated beam is allowed to drift so that the electrons in the beam become hunched. ln the reflex form of klystron, the beam is allowed to drift after emerging from grid 18a, and is gradually retarded and reversed by the reflector to re-enter the interaction space.V The returning beam, becoming hunched while drifting, imparts high frequency energy to the resonator, and the electrons in that beam are collected by the positive electrode structure represented by grids 16, 18, and 34.

By `diverting the returning -beam away from the course of the incoming beam produced by the gun, I have been successful in largely eliminating moding that hasbeen a persistent trouble in operation of reflex ltlystrons.V This moding seems to be largely eliminated by producing a magnetic eld transverse of the normal electron-beam path. My explanation for this effect is that the returning hunched electron-beam which 're-enters the interaction space 16a-18a, is prevented from interacting with the forward beam in the space between grid 34 and electron permeable wall portion 16a, and for this reason the for-v ward electron-beam entering the interaction space is not.

disturbed by the hunched electron-beam.

The bending of the electron beam is accomplished by means of an electromagnet in Figure l, including a sharp poled magnetic core 36 that is magnetized by a coil 38' adjustably energized with direct current from supply 40- and rheostat 42.

enter the interaction space 16a-18a.

between grid 18a and reflector 24, diverts the returning electrons to a path laterally off-set relative to the initial path A. Returning yelectron beam B :then re-enters the An. electron gun 22 is disposed at one side of the interactionv space 16a- 18a while at the opposite side of that inter Circuit connec tion to terminal 24a is provided by a button 26 supported' in an insulating plug 28 within cylinder 12 of the.-

ithermionic electron-emissivef cathode 30 and a beam forming and focusing shield 32;; and an electron permeable grid 34 extends across the,l path of the electronbeam between the cathode and the; interaction space 16a- 180, and acts as an anode for the: purpose of accelerating the electrons in the beam. Grid.'

the returning bunched electrons after their interactionV with the resonator.

The particular construction shown in Figure 1 for impressing a transverse magnetic eld on the interaction space is effective, but it will ybe apparent that such transverse magnetic eld can, in the alternative, be supplied by a magnet whose axis is parallel to the'electron path in the gun (Figure 2) butrwhosertield in the interaction space is curved so asV to be substantially perpendicular to the path of theelectron-beam.

The parts in Figure 2 are, with the exception of the magnetic structure, identical to those in Figure l and their description, therefore, is not repeated. However, in place of the'A electromagnet, a permanent magnet 36 is shown mounted in any convenient manner for adjustment along -the exterior of Iresonator wall 10. The magnetic iield represented by the dotted lines in Figure 2 is shown to extend, transverse of the electron path thru walls 16a and 18a; and while the eld must necessarily extend past the path of the beam in the region lof the gun and the Y reilector space, such elects'revidently contribute to the result described. -From Figure 3 it will be clear that the transverse eld is everywhere perpendicular Vto the plane of the beam that is curved by that magnetic field, being perhaps more effective in the drift 'space where the electrons remain for a relatively long portion 'of their travel time.

The theory of mode suppression as advanced above is what I presently consider correct. The substantial elimination of moding is in actual practice achieved when either orientation of magnet is employed.

The` yforegoing embodiments of the invention will naturally be found susceptible to -a latitude of varied design and application, and accordingly, the appended claims should be accorded that broad interpretation that is consistent with the spirit and scope of the invention.

What is claimed is:

1. A reex klystron including a cathode, beamrforming electrodes, a first perforate resonator wall, a second perloratel resonator wall, and a reector disposedV along an axis in the order named, and magnetic means normally thredlyV positioned adjacent said klystron to direct a substantial'electron-deection transverse magnetic -eidat the axis in the region of said perforate resonator walls.

Y 2. A klystron in accordancey with claim l, wherein Vsaid perforate electrodes and said rellector are symmetrical about said axis.

3. A klystron in accordance with claim 2, wherein the perforate region Iof said rst perforate resonator Wall -is of smaller transverse extent than-theperforate region of said second perforate resonator wall and said iirst perforate resonator wall embodies -an electron:y collecting imperforate areaY surrounding the perforate region, said im:v perforate area being opposed to afperforate wallgportion of the lsecond perfora-te Wall. i

4. A reflex klystron. in accordance. with;claimr1, wherein said magnet means comprises an electromagnet.

5. Apparatus in accordance with claim 1, wherein said magnetic means comprises an electromagnet extending transverse to the initial electron path in the region of said perforate resonator wall portions.

6. A reflex klystron in accordance with claimA l, wherein said magnetic means includes aV magnet disposed-ina position axially displaced from the perforatewalls` and; oiset in relation to the initial path of the electron-beam,V

whereby a magnetic field is established transversegof the electron-beamY path -in the region of the perforate wall' portions.

7. A reflex klystron including a pair of opposed electron permeable wal-ls and means including a cathode and reflecting means on opposite sidesiof the opposedrwalls for projecting an electron beam towards the walls and for.A reflecting the beam back toward the electron permeable walls, and magnetic means normally xedly positioned;

adjacent said klystron to direct a substantial electrondeection, the electron permable wall. adjacent. said cathode having van extensipnV positioned in the path of the returning reected electron. beam, said extensionbeingV an imperforate electrode structure.

References CitedV inthe tile ofA this patentV UNITED STATES PATENTS 1,564,070 Huppert Dec. l, 1925 2,259,690 Hansen et al Oct. 21 1941 2,411,913 Pierce et al Dec. 3, 1946 2,429,243 Snow et'al. Oct. 21, 1947' 2,460,402 Sziklai Feb'. 1, 1949 2,468,152 Woodyard Apr. 26, 1949.V V2,518,954 Steele Aug. 15, 1950 2,540,080 Janis Feb. 6, 1951 2,695,973 Ginzton Nov. 30, 19.547'

tra" 

